WASHINGTON — President Bush, seeking to recover some ground with his conservative base, today nominated Samuel Alito, a veteran judge and committed conservative, to replace U.S. Supreme Court Justice Sandra Day O'Connor.

Announcing his pick at the White House this morning, Bush emphasized that Alito, a former prosecutor and government attorney who has served as a federal appeals judge on the 3rd Circuit bench in Philadelphia for 15 years, has "more prior judicial experience than any Supreme Court nominee in more than 70 years."

The choice was in sharp contrast to Bush's last pick, Miers, who withdrew her nomination last Thursday after conservative Republicans complained she had no experience as a judge and lacked solid conservative credentials.

This time, Republicans are likely to rally behind the choice of a reliable conservative with impressive academic credentials and a long paper trail of cases and published decisions.

Conservative activist Gary Bauer, who had challenged Miers' nomination, said this time the fight will be with Democrats.

"At least now the president is having a battle with his political opponents and not with his friends," Bauer told CNN. "I will help him any way I can."

"Judge Alito is the best there is," said Wendy E. Long, counsel to the conservative Judicial Confirmation Network. "The Democrat-controlled Senate recognized these qualities in Judge Alito when it unanimously confirmed him to the court of appeals."

This time, though, Democrats have threatened to oppose, and possibly filibuster, any nominee deemed too far out of the mainstream. Alito, who is often derided as "Scalito," in reference to the Supreme Court's most vocal conservative, Justice Antonin Scalia, has a mixed record on abortion rights.

Senate Minority Leader Harry Reid, D-Nevada, who had suggested Miers to Bush, said the Senate needs to investigate whether Alito "is too radical for the American people."

Bush said Alito has shown "a mastery of the law, a deep commitment of justice, and he is a man of enormous character."

"He's scholarly, fair-minded and principled, and these qualities will serve our nation well on the highest court of the land," he said, adding that he hopes the Senate can confirm his choice by the end of the year.

With his wife and two children at his side, Alito said the Supreme Court, before which he has argued 12 cases, is "an institution I have long held in reverence."

After his White House introduction, Alito immediately headed to Capitol Hill where he was to greet Senate Majority Leader Bill Frist, R-Tenn., and pay his respects to the late civil rights pioneer Rosa Parks, whose coffin was lying in honor at the Capitol Rotunda.

Alito was the lone dissenter in Planned Parenthood v. Casey, a case in which the 3rd Circuit struck down a Pennsylvania law that included a provision requiring women seeking abortions to notify their spouses.

"The Pennsylvania legislature could have rationally believed that some married women are initially inclined to obtain an abortion without their husbands' knowledge because of perceived problems — such as economic constraints, future plans or the husbands' previously expressed opposition — that may be obviated by discussion prior to the abortion," Alito wrote.

The case ended up at the Supreme Court where the justices, in a 6-3 decision struck down the spousal notification provision of the law. The late Chief Justice William Rehnquist cited Alito's reasoning in his own dissent.

But in 2000, Alito joined the majority that found a New Jersey law banning late-term abortions unconstitutional. In his concurring opinion, Alito said the Supreme Court required such a ban to include an exception if the mother's health was endangered.

The high court is expected to decide later this year whether to hear a challenge to that decision.

Alito's selection is considered critical because he is replacing O'Connor, who has been the deciding vote in favor of abortion rights.

Alito, 55, was among Bush's favorite choices of the judges in the last set of deliberations, but he settled instead on White House counsel Miers, a Texan and longtime friend who came from outside what he called the "judicial monastery."

When Miers' nomination was withdrawn, Alito was at the top of the list.

Alito was nominated for his current job by Bush's father, former President George H.W. Bush, in 1990. Conservative supporters said his record shows a commitment to a strict interpretation of the Constitution and a defender of free speech and religious freedom.

Alito's nomination is the first step in Bush's political recovery plan as the White House struggles with a host of troubles. Besides the bungled Miers nomination, the White House is reeling from last week's indictment of Lewis "Scooter" Libby, Vice President Dick Cheney's chief of staff, on perjury and other charges in the CIA leak investigation.

Bush also has seen his approval rating drop to 39 percent, the lowest point of his presidency, as he faces criticism over the costly war in Iraq, rising fuel prices and the weak federal response to Hurricane Katrina.